Superconductor with improved flux pinning at low temperatures

ABSTRACT

A REBCO superconductor tape that can achieve a lift factor greater than or equal to approximately 3.0 or 4.0 in an approximately 3 T magnetic field applied perpendicular to a REBCO tape at approximately 30 K. In an embodiment, the REBCO superconductor tape can include a critical current density less than or equal to approximately 4.2 MA/cm2 at 77 K in the absence of an external magnetic field. In another embodiment, the REBCO superconductor tape can include a critical current density greater than or equal to approximately 12 MA/cm2 at approximately 30 K in a magnetic field of approximately 3 T having an orientation parallel to a c-axis.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/242,587, filed on Apr. 1, 2014, issuing on Oct. 27, 2020 as U.S. Pat.No. 10,818,416, which claims priority to U.S. provisional applicationSer. No. 61/807,142, filed on Apr. 1, 2013, both of which are herebyincorporated herein by reference in their entireties.

GOVERNMENT SPONSORSHIP

Advanced Research Projects Agency-Energy (ARPA-E), award DE-AR0000196

BACKGROUND

Several materials systems are being developed to solve the loomingproblems associated with energy generation, transmission, conversion,storage, and use. Superconductors are a unique system that provides asolution across a broad spectrum of energy problems. Superconductorsenable high efficiencies in generators, power transmission cables,motors, transformers and energy storage. Furthermore, superconductorstranscend applications beyond energy to medicine, particle physics,communications, and transportation.

Superconducting tapes are becoming more and more popular. This is inpart due to successful fabrication techniques that create epitaxial,single-crystal-like thin films on polycrystalline substrates (Y. Iijima,et al., Physica C 185, 1959 (1991); X. D. Wu, et al., Appl. Phys. Lett.67, 2397 (1995); A. Goyal, et. al., Appl. Phys. Lett. 69 (1996) p. 1795;V. Selvamanickam et al., “High Performance 2G wire: From R&D toPilot-scale Manufacturing,” IEEE Trans. Appl. Supercond. 19, 3225(2009)). In this technique, a thin film of materials having a rock saltcrystal structure (e.g., MgO) is deposited by ion-beam assisteddeposition over flexible, polycrystalline substrates. Superconductingfilms that are processed by this technique exhibit critical currentdensities comparable to that achieved in epitaxial films grown on singlecrystal substrates. Using this technique, several institutions havedemonstrated pilot-scale manufacturing of superconducting compositetapes. Remarkably, single crystal-like epitaxial films are now beingmanufactured at lengths exceeding 1 km using a polycrystalline substratebase.

One significant drawback of superconductors is that their ability tocarry current rapidly diminishes when the superconductor is exposed to amagnetic field. Thus, in certain applications such as wind generators,motors, high-field magnets, or energy storage systems, superconductorscannot achieve their full current carrying potential because thegenerator coil is exposed to magnetic fields at a few Tesla. Anotherdrawback is that in high-temperature superconductors (HTS),superconductivity is localized within the Cu—O planes (E. M. Gyorgy, et.al., “Anisotropic critical currents in Ba₂YCu₃O₇ analyzed using anextended bean model” Appl. Phys. Lett. 55, 283 (1989)). This phenomenoncreates an anisotropic effect in the superconductor's current carryingcapability. For example, FIG. 1 illustrates the anisotropy in criticalcurrent of a standard HTS tape made by a process called metal organicchemical vapor deposition (MOCVD). The anisotropic effect can bevisualized by aligning a magnetic field at different angles to the HTSfilm surface. The critical current drops rapidly as the field is movedaway from the film surface. Furthermore, the critical current reaches alow value when the field is oriented at a 0° angle from the tape normal(i.e. perpendicular to the tape surface). The critical current at thisfield orientation is the limiting value in the performance of coils thatare constructed with these standard tapes.

Over the last decade research has been focused on improving the currentcarrying capabilities of superconductors exposed to a magnetic field.Significant research has been focused on improving flux pinning insuperconductors. Flux pinning is a phenomenon of type IIhigh-temperature superconductors (HTS), which unlike Type Isuperconductors, have two critical fields that allow partial penetrationof a magnetic field. Above the lower critical field, 2G HTS tapes allowmagnetic flux to penetrate the superconducting film in quantized packetssurrounded by a superconducting current vortex through flux tubes. Atlower currents, the flux tubes are pinned in place. This pinningphenomenon can substantially reduce any flux creeping that can createundesirable electrical resistance in the superconductor. Thus,improvements to flux pinning can minimize the above drawbacks that asuperconductor experiences in a magnetic field (e.g., anisotropy, lowercritical current, etc.).

The most explored strategy to improve flux pinning has been to introducedefects into the superconductor that are comparable in lateraldimensions with superconducting coherence length since the lateral sizeof the penetrated flux lines is equal to twice the value of thecoherence length. In 2G HTS tapes, defects include oxygen vacancies,threading dislocations, twin planes, impurity atoms, irradiation-inducedcolumnar defects, and nanostructured inclusions, of various compositionand structure (V. M. Pan, et al., “Dimensional crossovers and relatedflux line-lattice states in YBa₂Cu₃O₇-δ,” Physica C 279, 18 (1997); J.M. Huijbregtse, et al., “Vortex pinning by natural defects in thin filmsof YBa₂Cu₃O₇-δ,” Supercond. Sci. Technol. 15, 395 (2002); G. Blatter, etal., “Vortices in high-temperature superconductors,” Rev. Mod. Phys. 661125 (1994); L. Civale, “Vortex pinning and creep in high-temperaturesuperconductors with columnar defects,” Supercond. Sci. Technol. 10, All(1997); C. J. van der Beek, et al., “Strong pinning in high-temperaturesuperconducting films,” Phys. Rev. B 66, 024523 (2003)). Particularly,irradiation-induced columnar defects have shown great potential forimproving flux pinning. Research groups have recently developed anapproach to introduce columnar defects by chemically doping asuperconducting film with BaZrO₃ (BZO) or BaSnO₃ (BSO) (J. L.Macmanus-Driscoll et al., “Strongly enhanced current densities insuperconducting coated conductors of YBa₂Cu₃O₇−x+BaZrO₃,” NatureMaterials 3, 439 (2004); S. Kang et al. “High-Performance High-TcSuperconducting Wires,” Science 311, 1911 (2006); Y. Yamada et al.,“Epitaxial nanostructure and defects effective for pinning inY(RE)Ba₂Cu₃O₇−x coated conductors,” Appl. Phys. Lett. 87, 132502 (2005);C. Varanasi, et al., “Thick YBa₂Cu₃O₇−x+BaSnO₃ films with enhancedcritical current density at high magnetic fields,” Appl. Phys. Lett. 93092501, (2008)). The BZO and BSO inclusions formed nano-sized columns(about 5 nm in diameter) by a self-assembly process duringsuperconductor film growth, which significantly improved the film'spinning strength (S. Kang et al. “High-Performance High-TcSuperconducting Wires,” Science 311, 1911 (2006); Y. Yamada et al.,“Epitaxial nanostructure and defects effective for pinning inY(RE)Ba₂Cu₃O₇−x coated conductors,” Appl. Phys. Lett. 87, 132502 (2005);C. Varanasi, et al., “Thick YBa₂Cu₃O₇−x+BaSnO₃ films with enhancedcritical current density at high magnetic fields,” Appl. Phys. Lett. 93092501, (2008); T. Horide, et al., “The crossover from the vortex glassto the Bose glass in nanostructured YBa₂Cu₃O₇−x films,” Appl. Phys.Lett. 82, 182511 (2008); M. Mukaida, et al., “Critical Current DensityEnhancement around a Matching Field in ErBa₂Cu₃O₇−δ Films with BaZrO₃Nano-Rods,” Jpn. J. Appl. Phys. 44, L952 (2005)).

FIG. 2 displays a cross sectional microstructure of a (Gd,Y)Ba₂Cu₃O_(x)(Gd—YBCO) film grown by MOCVD with BZO nanocolumns mostly orientedperpendicular to the film plane. As shown in FIG. 1, films doped withBZO exhibit two-fold improved performance in a magnetic field of 1 Teslaat 77 K, especially when exposed to fields oriented along the directionof the BZO nanocolumns (i.e., perpendicular to the tape). Also, sincethe nanocolumns exhibit a splay about the film growth direction,improved pinning is observed over a range of field orientations.Finally, BZO-doped films exhibit a significantly lower anisotropy (V.Selvamanickam et al., “Influence of Zr and Ce Doping on ElectromagneticProperties of (Gd,Y)—Ba—Cu—O Superconducting Tapes Fabricated by MetalOrganic Chemical Vapor Deposition,” Physica C 469, 2037 (2009)).

Most research focused on BZO-doped REBCO (RE=rare earth) tapes hasreported critical currents in a magnetic field of 1-3 Tesla at 77 K. Atleast one research group has reported critical currents in high magneticfields up to 30 T at 4.2 K (V. Braccini, et al., “Properties of recentIBAD-MOCVD Coated Conductors relevant to their high field, lowtemperature magnet use,” Superconductor Science and Technology 24,035001 (2011)). Unfortunately, there is little to no research reportingcritical currents in practical magnetic fields of a few Tesla atintermediate temperatures of 20 to 50 K. Yet a number of 2G HTSapplications such as wind generators, utility generators, marine motors,and industrial motors are being developed in these latter magneticfields and intermediate temperature ranges (A. B. Abrahamsen, et al.,“Feasibility study of 5 MW superconducting wind turbine generator,”Physica C.471, 1464-69 (2011); P. Kummeth, et al., “Development ofsynchronous machines with HTS rotor,” Physica C.426, 1358-64 (2005)).

It was recently demonstrated that the level of Zr needed to achieve atwo-fold improvement in REBCO performance in a 1 T magnetic field at 77K did not achieve the same improvement in the more practical magneticfield of a few Tesla at 20K to 50 K (hereafter “practical conditions”)(V. Selvamanickam, et al., “Enhanced critical currents in high levels ofZr-added (Gd,Y)Ba₂Cu₃Ox superconducting tapes,” Supercond. Sci. Technol.26, 035006 (2013)). But it was also shown in the same publication that ahigher level of Zr does in fact lead to an improvement in REBCOperformance under the practical conditions (V. Selvamanickam, et al.,“Enhanced critical currents in high levels of Zr-added (Gd,Y)Ba₂Cu₃Oxsuperconducting tapes,” Supercond. Sci. Technol. 26, 035006 (2013)).Particularly, the film's ‘lift factor’ (typically around 2.1 at 30 K, 3T) is substantially improved with higher levels of Zr addition. ‘Liftfactor’ refers to the ratio of the tape's critical current under thepractical conditions to the critical current of the tape in a zeromagnetic field at 77 K. It was also recently demonstrated that a highcritical current density (a generally sought after superconductorperformance goal) can be achieved in REBCO tapes with high levels of Zraddition at 77 K (V. Selvamanickam, et al., “Low-temperature, HighMagnetic Field Critical Current Characteristics of Zr-added(Gd,Y)Ba₂Cu₃O_(x) superconducting tapes,” Supercond. Sci. Technol. 25,125013 (2012)). These findings opened up the possibility that dopingREBCO tapes with substantially high levels of Zr could produce both highcritical current densities and high lift factors under the practicalconditions. However, it has been found that the lift factors of REBCOtapes with high levels of added Zr are substantially inconsistent.

Thus, there is need in the art for methods and compositions that canachieve in a superconductor both a high lift factor and high criticalcurrent density under practical operating conditions.

SUMMARY

A summary of certain embodiments disclosed herein is set forth below.It's understood that this section is presented merely to provide thereader with a brief summary of certain embodiments and that thesedescriptions are not intended to limit this application's scope.

Indeed, this disclosure may encompass a variety of embodiments that maynot be set forth herein.

A superconducting tape can be fabricated to achieve a high lift factorin an approximately 3 T magnetic field applied perpendicular to the tapeat approximately 30 K. In one embodiment, a superconducting tape can befabricated to achieve a lift factor greater than 3.0 or greater than 4.0in an approximately 3 T magnetic field applied perpendicular to a REBCOtape at approximately 30 K.

In another embodiment, a superconducting tape is fabricated to include acritical current density less than or equal to approximately 4.2 MA/cm²at 77 K in the absence of an external magnetic field. In yet anotherembodiment, the superconducting tape is fabricated to include a criticalcurrent density greater than or equal to approximately 12 MA/cm² atapproximately 30 K in a magnetic field of approximately 3T having anorientation parallel to the c-axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description,will be better understood when read in conjunction with the appendeddrawings. For the purpose of illustration only, there is shown in thedrawings certain embodiments. It's understood, however, that theinventive concepts disclosed herein are not limited to the precisearrangements and instrumentalities shown in the figures.

FIG. 1 illustrates critical current density as a function of an anglebetween a magnetic field and substrate tape normal for an MOCVD HTS tapeand BZO-doped MOCVD tape.

FIG. 2 illustrates a cross-sectional microstructure of Zr-dopedsuperconducting film synthesized by MOCVD.

FIG. 3 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes of various compositions as measuredby ICP spectroscopy of the films, in accordance with an embodiment.

FIG. 4 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes as a function of barium expressed asan atomic percent of all cations (Gd, Y, Ba, Cu, Zr) in the film, inaccordance with an embodiment.

FIG. 5 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes as a function of zirconium expressedas an atomic percent of all cations (Gd, Y, Ba, Cu, Zr) in the film, inaccordance with an embodiment.

FIG. 6 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes as a function of barium+zirconiumexpressed as an atomic percent of all cations (Gd, Y, Ba, Cu, Zr) in thefilm, in accordance with an embodiment.

FIG. 7 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes as a function of copper expressed asan atomic percent of all cations (Gd, Y, Ba, Cu, Zr) in the film, inaccordance with an embodiment.

FIG. 8 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes of various compositions as measuredby ICP spectroscopy of the films, in accordance with an embodiment.

FIG. 9 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes as a function of barium to copperratio in the film, in accordance with an embodiment.

FIG. 10 illustrates lift factors in a magnetic field of 3 T at 30 K of15-25 mol. % Zr-added GdYBCO tapes as a function of barium+zirconium tocopper ratio in the film, in accordance with an embodiment.

FIG. 11 illustrates lift factors in a magnetic field of 3 Tesla at 30 Kof 15-20 mol. % Zr-added GdYBCO tapes as a function of critical currentdensity at 77 K in zero magnetic field.

DETAILED DESCRIPTION

Before explaining at least one embodiment in detail, it should beunderstood that the inventive concepts set forth herein are not limitedin their application to the construction details or componentarrangements set forth in the following description or illustrated inthe drawings. It should also be understood that the phraseology andterminology employed herein are merely for descriptive purposes andshould not be considered limiting.

It should further be understood that any one of the described featuresmay be used separately or in combination with other features. Otherinvented systems, methods, features, and advantages will be or becomeapparent to one with skill in the art upon examining the drawings andthe detailed description herein. It's intended that all such additionalsystems, methods, features, and advantages be protected by theaccompanying claims.

It is one objective of the embodiments described herein to fabricate asuperconducting tape that can consistently achieve a lift factor of atleast approximately 3.0 in an approximately 3 T magnetic field appliedperpendicular to a REBCO tape at approximately 30 K. It is anotherobjective of the embodiments described herein to fabricate asuperconducting tape that can consistently achieve a lift factor of atleast approximately 4.0 in an approximately 3 T magnetic field appliedperpendicular to a REBCO tape at approximately 30 K. In one embodiment,the REBCO tape is fabricated by MOCVD.

In an embodiment, the REBCO tape may include a substrate, a buffer layeroverlying the substrate, a superconducting film followed by a cappinglayer (typically a noble metal), and a stabilizer layer (typically anon-noble metal such as copper). The buffer layer may consist of severaldistinct films.

In one embodiment, the substrate may include a metal alloy that canwithstand high temperatures, such as nickel-based or iron-based alloys.Examples may include Hastelloy®, Inconel® group of alloys, stainlesssteel alloys, or nickel-tungsten and nickel-chromium alloys. Thesubstrate may typically be in the form of a thin tape, approximately 25to 100 μm thick, approximately 2 mm to 100 mm wide, and approximately 1to 10,000 meters long. The substrate can be treated by techniques suchas polishing to produce a smooth surface with an approximately 0.5 to 20nm surface roughness. Additionally, in another embodiment, the substratemay be treated to be biaxially textured, such as by the known RABiTS(rolling assisted biaxially textured substrate) technique.Alternatively, in yet another embodiment, the substrate may be anon-textured polycrystalline, such as commercially available Hastelloy®,Inconel® group of alloys, and stainless steel alloys.

In another embodiment, the buffer layer may be a single layer, or morecommonly, be made up of several films. In yet another embodiment, thebuffer layer may include a biaxially textured film, having a crystallinetexture that is generally aligned along crystal axes both in-plane andout-of-plane of the film. Such biaxial texturing may be accomplished byion beam assisted deposition (IBAD). For example, IBAD can be used toform a biaxially-textured buffer layer to produce a superconductinglayer having desirable crystallographic orientation for superiorsuperconducting properties.

In an embodiment, magnesium oxide can be used as a film for the IBADfilm, and may be on the order of approximately 1 to approximately 500nm, such as approximately 5 to approximately 50 nanometers. The bufferlayer may also include additional films, such as a barrier film providedto directly contact and be placed in between an IBAD film and thesubstrate. In this embodiment, the barrier film may be an oxide, such asalumina or zirconates (e.g., yttria stabilized zirconia, gadoliniumzirconate, etc.), and can function to isolate the substrate from theIBAD film. Typical thicknesses of the barrier film may be within a rangeof approximately 1 to approximately 200 nm.

Still further, in yet another embodiment, the buffer layer may alsoinclude an epitaxially grown film(s) such as LaMnO₃, SrTiO₃, CeO₂,formed over the IBAD film. An epitaxially grown film can help toaccommodate the lattice mismatch between MgO and REBCO. In otherembodiments, all buffer films may be deposited by various physical vapordeposition, solution coating, or chemical vapor deposition techniques.

In an embodiment, the superconducting REBCO film may consist of a singlerare-earth element such as yttrium, gadolinium, neodymium, erbium,europium, samarium, dysprosium, holmium. In another embodiment, thesuperconducting REBCO film may consist of one or more of theserare-earth elements, in any combination. The superconducting film may beapproximately 0.5 to 10 μm thick. In still another embodiment, the REBCOfilm can be deposited via a thin film physical vapor depositiontechnique (e.g., pulsed laser deposition (PLD)), evaporation orsputtering, chemical vapor deposition (CVD), or chemical solutiondeposition (CSD).

In addition to the constituent RE, Ba, Cu cations, in anotherembodiment, dopant materials can be added to the starting sourcematerial incorporated in the superconducting film to improve fluxpinning. In one embodiment, if the superconducting film is made by PLDor sputtering, one or more dopants such as BaZrO₃, BaSnO₃, BaHfO₃,BaTiO₃, BaCeO₃, REBa₂NbO₆, REBa₂TaO₆, CeO₂, ZrO₂, or YSZ can be mixedwith the precursors to form a target for ablation. Alternatively, inanother embodiment, the dopants may be made as a segment of a target ormay be made into a separate target.

In an embodiment, as an ablation laser, such as an excimer laser, scansover the target(s), the REBCO and dopant material can be depositedtogether to form a film on the buffered substrate. Alternatively, inanother embodiment, if the superconducting film is made by evaporation,the dopant material may be added in the source as a separate element,such as Zr, Ce, Ti, Nb, Hf, Ta, and Sn.

In one embodiment, the superconducting film may be made by a chemicaldeposition process, such as metal organic chemical vapor deposition(MOCVD), metal organic deposition (MOD), or chemical solution deposition(CSD). In these embodiments, the dopants, such as Zr, Ce, Ti, Nb, Hf,Ta, and Sn, can be added as metal organics in the starting precursor.For example, the dopant can be added in the form of tetramethylheptanedionate (thd) in the case of MOCVD, or as acetates or acetylacetonates in the case of MOD or CSD. A solution of all precursors canbe made using a solvent such as tetrahydofuran (THF) in the case ofMOCVD, and trifluoroacetic acid (TFA) in the case of MOD or CSD.

In an embodiment, in the MOCVD process, the REBCO precursor solution anddopant precursor solution may be mixed together and delivered in avaporizer as a single solution. Alternatively, the REBCO precursorsolution and dopant precursor solution can be delivered in a vaporizeras separate solutions. In another embodiment, the vaporized precursorscontaining the RE, Ba, Cu and dopant are delivered by means of a carriergas, such as argon. The precursors can then be mixed with oxygen gas andtogether injected into an MOCVD reactor through a showerhead. In yetanother embodiment, the precursor vapor can be deposited on the bufferedsubstrate that is heated by means of a resistive or radiative heater.The result is a REBCO film with an embedded oxide of the dopantcompound. In still another embodiment, using Zr dopant causes BZO toform in the REBCO film. It has been found that BZO and other dopantmaterials form as nanocolumns or other nanostructures in the REBCO film,thereby enabling improved flux pinning (V. Selvamanickam, et al.,“Influence of Zr and Ce Doping on Electromagnetic Properties of(Gd,Y)—Ba—Cu—O Superconducting Tapes Fabricated by Metal OrganicChemical Vapor Deposition,” Physica C 469, 2037 (2009); V.Selvamanickam, et al., “Enhanced critical currents in high levels ofZr-added (Gd,Y)Ba₂Cu₃O_(x) superconducting tapes,” Supercond. Sci.Technol. 26, 035006 (2013); V. Selvamanickam, et al., “Low-temperature,High Magnetic Field Critical Current Characteristics of Zr-added(Gd,Y)Ba₂Cu₃O_(x) superconducting tapes,” Supercond. Sci. Technol. 25,125013 (2012)).

In another embodiment, the REBCO tape may also include a capping layerand a stabilizer layer, which can be implemented to provide a lowresistance interface and electrical stabilization to help preventsuperconductor burnout during practical use. In yet another embodiment,a noble metal can be used as the capping layer to prevent unwantedinteractions between the stabilizer layer(s) and the superconductinglayer. Some noble metals may include gold, silver, platinum, andpalladium. In an embodiment, the capping layer may be approximately 0.01μm to approximately 20 μm thick, or approximately 1 μm thick toapproximately 3 μm thick. The capping layer can be deposited bysputtering, evaporation, or electrodeposition.

In one embodiment, the stabilizer layer may function as aprotection/shunt layer to enhance stability against harsh environmentalconditions and superconductivity quench. The layer may be dense andthermally and electrically conductive, and can function to bypasselectrical current in case of failure of the superconducting layer or ifthe critical current of the superconducting layer is exceeded. It mayalso be formed by any one of various thick and thin film formingtechniques, such as by laminating a pre-formed copper strip onto thesuperconducting tape, or by using an intermediary bonding material suchas a solder.

In one embodiment, the composition of the superconducting film (withoutthe capping and stabilizer layers) can be measured via ICP spectroscopy.In another embodiment, the critical current density of thesuperconducting tape can be measured by a four probe technique at 77 K,in a zero applied magnetic field, and in the presence of variousmagnetic fields at temperatures between approximately 4.2 K and 77 K. Inanother embodiment, the in-field critical current measurement may beperformed with the orientation of magnetic field parallel as well asperpendicular to the tape normal. Additionally, in yet anotherembodiment, the critical current density may be measured at intermediatemagnetic field orientations. The lift factor at any temperature andmagnetic field can be calculated as the ratio of the critical current ofthe tape at that condition to the critical current at 77 K in a zeroapplied magnetic field.

Referring to FIG. 3, by way of example only, in one embodiment the liftfactors of various superconductor film compositions in an approximately3 T magnetic field at approximately 30 K can be mapped over acomposition range of approximately 15.0% to approximately 24.5% of RE(Gd+Y), approximately 29.0% to approximately 38.5% Ba+Zr, andapproximately 46.5% to approximately 56.0% Cu. These films can befabricated by a MOCVD process using tetramethyl heptanedionateprecursors of Gd, Y, Ba, and Cu, mixed in a THF solvent. The precursorrecipe can include an additional 15 to 25 mol. % Zr. If all the cations(RE, Ba, Cu, Zr) in the precursor are incorporated in the film, 15% Zrmay correspond to a Zr content equal to 2.4 atomic % of all cations inthe film. The solution can be flash vaporized at about 270° C. and theprecursors deposited on a LaMnO₃-buffered MAD MgO-based Hastelloysubstrate. The deposition can be conducted at a temperature of 750 to850° C. at a pressure of 2 to 3 Torr.

As illustrated in FIG. 3, in an embodiment, superconducting tapes havinga barium+zirconium content greater than approximately 32.0 atomic % anda copper content less than approximately 49.0 atomic %, can exhibit alift factor greater than approximately 3.0 in an approximately 3 Tmagnetic field at approximately 30 K. In one embodiment, for samplesexhibiting a lift factor above approximately 3.0 at approximately 3 T atapproximately 30 K, the Zr content in the film may be at least 1.65atomic %, and the barium content may be at least 29.9%. In anotherembodiment, superconducting tapes having a barium+zirconium contentgreater than approximately 33.0 atomic %, a copper content less thanapproximately 49.0% atomic %, can exhibit a lift factor greater thanapproximately 4.0 in an approximately 3 T magnetic field atapproximately 30 K. In one embodiment, for samples exhibiting a liftfactor above approximately 4.0 at approximately 3 T at approximately 30K, the Zr content in the film may be at least 1.65 atomic %, and thebarium content may be at least 30.5 atomic %.

The limiting values of barium, zirconium, barium+zirconium, and copperin the film to achieve a lift factor greater than approximately 3.0 andapproximately 4.0 in an approximately 3 T field at approximately 30 Kare illustrated, by way of example only, in FIGS. 4, 5, 6 and 7,respectively. For example, FIG. 4 illustrates the limiting value ofbarium necessary to achieve a lift factor greater than approximately 3.0in an approximately 3 T field at approximately 30 K. In one embodiment,Ba content greater than approximately 29.9 at. % can achieve a liftfactor above 3. In another embodiment, Ba content greater thanapproximately 30.5 at. % can achieve a lift factor above 4. FIG. 5, byway of example only, illustrates the limiting value of zirconiumnecessary to achieve a lift factor greater than approximately 3.0 andapproximately 4.0 in an approximately 3 T field at approximately 30 K.In one embodiment, Zr content greater than approximately 1.65 at. % canachieve a lift factor above both 3 and 4. FIG. 6, by way of exampleonly, illustrates the limiting value of barium+zirconium necessary toachieve a lift factor greater than approximately 3.0 and approximately4.0 in an approximately 3 T field at approximately 30 K. In oneembodiment, Ba+Zr content greater than approximately 31.5 at. % canachieve a lift factor above 3. In another embodiment, Ba+Zr contentgreater than approximately 33.0 at. % can achieve a lift factor above 4.FIG. 7, by way of example only, illustrates the limiting value of coppernecessary to achieve a lift factor greater than approximately 3.0 andapproximately 4.0 in an approximately 3 T field at approximately 30 K.In one embodiment, Cu content less than approximately 51.0% at. % canachieve a lift factor above 3. In another embodiment, Cu content lessthan approximately 50.0 at. % can achieve a lift factor above 4.

Referring to FIG. 8, by way of example only, in one embodiment the liftfactors in an approximately 3 T magnetic field at approximately 30 K ofvarious superconductor film compositions normalized to the Ba+Zr+Cuvalues can be mapped over a composition range of approximately 1.0% toapproximately 10.0% of Zr, approximately 34.0% to approximately 43.0%Ba, and approximately 56.0% to approximately 65.0% Cu.

As illustrated in FIG. 8, in an embodiment, superconducting tapes havinga barium content greater than approximately 37.5% of the total contentof Ba+Cu+Zr, a copper content less than approximately 60.5% of the totalcontent of Ba+Cu+Zr, and a zirconium content less than approximately 2%of the total content of Ba+Cu+Zr can exhibit a lift factor greater thanapproximately 3.0 in an approximately 3 T magnetic field atapproximately 30 K. In another embodiment, superconducting tapes havinga barium content greater than approximately 38% of the total content ofBa+Cu+Zr, a copper content less than approximately 59.5% of the totalcontent of Ba+Cu+Zr, and a Zr content less than approximately 2.5% ofthe total content of Ba+Cu+Zr can exhibit a lift factor greater thanapproximately 4.0 in an approximately 3 T magnetic field atapproximately 30 K.

The ratios of barium to copper and barium+zirconium to copper in thefilm to achieve a lift factor greater than approximately 3 andapproximately 4 in an approximately 3 T field at approximately 30 K areillustrated, by way of example only, in FIGS. 9 and 10, respectively.For example, FIG. 9 illustrates the ratio of barium to copper necessaryto achieve a lift factor greater than approximately 3.0 in anapproximately 3 T field at approximately 30 K. In one embodiment, a Bato Cu ratio greater than or equal to at least approximately 0.58 canachieve a lift factor above 3. In another embodiment, a Ba to Cu ratiogreater than or equal to at least approximately 0.62 can achieve a liftfactor above 4. FIG. 10, by way of example only, illustrates the ratioof barium+zirconium to copper necessary to achieve a lift factor greaterthan approximately 3 and approximately 4 in an approximately 3 T fieldat approximately 30 K. In one embodiment, a Ba+Zr to Cu ratio greaterthan or equal to at least approximately 0.62 can achieve a lift factorabove 3. In another embodiment, a Ba+Zr to Cu content greater than orequal to at least approximately 0.65 can achieve a lift factor above 4.

FIG. 11 illustrates the lift factors of several (Gd, Y)—Ba—Cu—O tapeswith approximately 15 to 25 mol. % Zr addition in a magnetic field ofapproximately 3 Tat approximately 30 K (applied perpendicular to thetape) having a range of critical current densities (J_(c)) (e.g., 2 to 5MA/cm²) in a magnetic field of 0 T at 77 K. Unexpectedly, only thosesuperconducting tapes having a critical current density less than 4.2MA/cm² in a 0 T magnetic field at 77 K may exhibit a lift factor greaterthan approximately 3.0 in an approximately 3 T magnetic field atapproximately 30 K. Furthermore, only those superconducting tapes havinga critical current density less than 3.8 MA/cm² in a 0 T magnetic fieldat 77 K may exhibit a lift factor greater than approximately 4.0 in anapproximately 3 T magnetic field at approximately 30 K. The trend insuperconductor research has been to increase the critical currentdensity at 77 K in zero magnetic field. Therefore, the finding that ahigher critical current density at 77 K in a zero magnetic field may beundesirable from the point of view of achieving a high lift factor inpractical conditions is unexpected and has not previously been foreseenin the art.

It is another objective of the application to achieve in asuperconductor tape both a lift factor greater than approximately 3.0and a high absolute critical current density value in an approximately 3T magnetic field at approximately 30 K. In one embodiment, the criticalcurrent density of the tape in an approximately 0 T magnetic field atapproximately 77 K can be high enough to achieve a critical currentdensity over approximately 800 A/cm-width in an approximately 3 Tmagnetic field at approximately 30 K. For example, an approximately 0.91μm thick superconducting film with cation composition of approximately30.17% Ba, approximately 50.7% Cu, approximately 8.86% Y, approximately7.5% Gd, and approximately 1.77% Zr, may exhibit a critical currentdensity of approximately 2.76 MA/cm² at 77 K, 0 T and a lift factor ofapproximately 3.4 at approximately 30 K and approximately 3 T.Accordingly, the critical current of the tape may be approximately 851A/cm at approximately 30 K and approximately 3 T. In still a furtherembodiment, superconducting tapes having a barium+zirconium contentgreater than approximately 31.5 atomic %, a copper content less thanapproximately 51 atomic %, and a rare earth (e.g. yttrium+gadolinium)content less than approximately 19.5 atomic % can exhibit a criticalcurrent density over approximately 800 A/cm-width in an approximately 3T magnetic field at approximately 30 K.

In another embodiment, the above identified correlation between criticalcurrent density and lift factor may be observed at temperatures belowapproximately 60 K. For example, an opproximately 0.85 μm thicksuperconducting film may exhibit a critical current density ofapproximately 3.16 MA/cm² at 77 K, 0 T and at 3 T, lift factors ofapproximately 1.25 at 59 K, 1.57 at 54 K, 1.90 at 49 K, 2.99 at 38 K,4.1 at 30 K, 4.64 at 25 K, and 5.67 at 20 K. In yet another embodiment,a superconducting film with a film thickness of approximately 0.91 μmmay exhibit a critical current density of approximately 4.66 MA/cm² at77 K, 0 T and at 3 T, lift factors of approximately 0.61 at 59 K, 0.77at 54 K, 0.92 at 49 K, 1.29 at 39 K, 1.68 at 30 K, 1.90 at 25 K, and2.21 at 20 K.

In yet another embodiment, a similar correlation may exist between thesuperconducting tape composition and lift factor at temperatures belowapproximately 60 K. For example, a 0.85 μm thick superconducting filmwith cation composition of approximately 31.49% Ba, approximately 50.88%Cu, approximately 8.56% Y, approximately 7.3% Gd, and approximately1.75% Zr, may exhibit a critical current density of approximately 3.16MA/cm² at 77 K, 0 T and at 3 T, lift factors at approximately 1.25 at 59K, 1.57 at 54 K, 1.90 at 49 K, 2.99 at 38 K, 4.1 at 30 K, 4.64 at 25 K,and 5.67 at 20 K.

The Ba+Zr-Cu ratio can have the strongest impact on lift factor. Thus,in other embodiments, the superconducting REBCO tape may include one ofthe following RE elements: Y, Gd, Dy, Ho, Er, Tb, Yb, Eu, Nd, or Sm. Foreach type of superconducting tape, there may be a similar correlationbetween critical current density and lift factor, as observed in FIGS. 3and 11. For example, an approximately 0.91 μm thick superconducting filmof (Gd,Dy)—Ba—Cu—O composition with Zr doping may exhibit a criticalcurrent density of approximately 2.61 MA/cm² at 77 K, 0 T and a liftfactor of approximately 3.0 at approximately 30 K and approximately 3 T.

It is yet another objective of the application to achieve in asuperconductor tape both a lift factor greater than approximately 4.0and a high absolute critical current density value in an approximately 3T magnetic field at approximately 30 K. In one embodiment, the criticalcurrent density of the tape in an approximately 0 T magnetic field atapproximately 77 K can be high enough to achieve a critical current overapproximately 2160 A/12 mm-width in an approximately 3 T magnetic fieldat approximately 30 K. For example, the below table 1 illustrates thecritical current densities and lift factors of various 0.9 μm thicksuperconducting films having different approximated cation compositions.

TABLE 1 Lift Factors of REBCO Superconducting Films Jc Lift factor JcTape Cu Y Zr Ba Gd (77 K, (30 K, (30 K, # % % % % % 0 T) 3 T) 3 T) 149.6 9.4 1.7 31.3 8.0 2.84 4.39 12.47 2 47.2 9.7 3 31.1 9.1 3.54 4.5816.21 3 47.5 9.8 2.4 31.1 9.2 3.76 4.09 15.38 4 46.6 9.1 2.4 33.3 8.61.93 6.22 12.01 5 46.7 9.6 3.3 31.3 9.1 2.30 5.69 13.09 6 47.2 9.2 2.532.3 8.8 3.10 6.45 20.0

Accordingly, the critical current of tape 1 may be approximately 1346A/12 mm at approximately 30 K and approximately 3 T. The criticalcurrent of tape 2 may be approximately 1751 A/12 mm at approximately 30K and approximately 3 T. The critical current of tape 3 may beapproximately 1661A/12 mm at approximately 30 K and approximately 3 T.The critical current of tape 4 may be approximately 1297 A/12 mm atapproximately 30 K and approximately 3 T. The critical current of tape 5may be approximately 1413 A/12 mm at approximately 30 K andapproximately 3 T. And the critical current of tape 6 may beapproximately 2160 A/12 mm at approximately 30 K and approximately 3 T.

Other dopants can work equally as well as Zr. Thus, in still otherembodiments, the superconducting tapes are doped with one or more of thefollowing constituents: niobium, tantalum, hafnium, tin, cerium andtitanium. For each type of superconducting tape, there may be a similarcorrelation between critical current density and lift factor, asobserved in FIGS. 3 and 11.

It's understood that the above description is intended to beillustrative, and not restrictive. The material has been presented toenable any person skilled in the art to make and use the inventiveconcepts described herein, and is provided in the context of particularembodiments, variations of which will be readily apparent to thoseskilled in the art (e.g., some of the disclosed embodiments may be usedin combination with each other). Many other embodiments will be apparentto those of skill in the art upon reviewing the above description. Thescope of the invention therefore should be determined with reference tothe appended claims, along with the full scope of equivalents to whichsuch claims are entitled. In the appended claims, the terms “including”and “in which” are used as the plain-English equivalents of therespective terms “comprising” and “wherein.”

EXAMPLES

A Hastelloy C-276 tape with alumina and yttria buffer layers was coatedwith MgO by ion beam assisted deposition (IBAD) at room temperature toyield biaxially-textured film. Homo-epitaxial MgO and LaMnO₃ weredeposited on the IBAD MgO layer by magnetron sputtering in a temperaturerange of 600 to 800° C. The buffered tape was used for MOCVD of GdYBCOfilm with Zr addition. Tetramethyl heptanedionate precursors with acation composition of Zr_(0.15)Gd_(0.6)Y_(0.6)Ba₂Cu_(2.3) were dissolvedin a solvent of tetrahydrofuran at a molarity of 0.05 M/L. The precursorsolution was delivered at a flow rate of 2.5 mL/min, flash vaporized at270° C. and carried in a gas of argon, mixed with oxygen and theninjected into the reactor using a linear showerhead. The precursor vaporwas deposited at temperature range of approximately 830° C. at a reactorpressure of 2.3 Torr on the buffered IBAD tape moving at a speed of 2.1cm/min. The thickness of the superconductor film was measured bycross-sectional transmission electron microscopy to be 0.925 μm. Thecation atomic composition of the film was determined by ICPspectroscopic analysis to be 31.35% Ba, 49.57% Cu, 8.03% Gd, 9.36% Y and1.69% Zr. The critical current density of the tape was measured to be2.84 MA/cm² at 77 K, 0 T. At 30 K and a 3 T field applied perpendicularto the tape, a lift factor of 4.4 was achieved corresponding to acritical current of 1153 A/cm.

Tetramethyl heptanedionate precursors with a cation composition ofZr_(0.15)Gd_(0.6)Y_(0.6)Ba₂Cu_(2.2) were dissolved in a solvent oftetrahydrofuran at a molarity of 0.05 M/L. The precursor solution wasdelivered at a flow rate of 2.5 mL/min, flash vaporized at 270° C. andcarried in a gas of argon, then mixed with oxygen and injected into thereactor using a linear showerhead. The precursor vapor was deposited attemperature range of approximately 800° C. at a reactor pressure of 2.3Torr on the buffered MAD tape moving at a speed of 2.1 cm/min. Thethickness of the superconductor film was measured by cross-sectionaltransmission electron microscopy to be 0.91 μm. The cation atomiccomposition of the film was determined by ICP spectroscopic analysis tobe 30.29% Ba, 51.47% Cu, 8.12% Gd, 8.55% Y and 1.57% Zr. The criticalcurrent density of the tape was measured to be 4.37 MA/cm² at 77 K, 0 T.At 30 K and a 3 T field applied perpendicular to the tape, a lift factorof 1.8 was achieved corresponding to a critical current of 728 A/cm.

What is claimed is:
 1. A method of manufacturing a REBCO superconductingtape comprising: applying to a superconducting tape substrate aprecursor vapor, the precursor vapor resulting in a film comprising: abarium+dopant content greater than approximately 32.0 atomic %; and acopper content less than approximately 49.0 atomic %.
 2. The method ofclaim 1, wherein the superconducting tape further comprises a liftfactor greater than or equal to approximately 3.0 at approximately 30 Kin a magnetic field of approximately 3 T having an orientationperpendicular to the superconducting tape.
 3. The method of claim 2,wherein the copper content is less than approximately 48.5 atomic % andthe film further comprises a rare-earth content between 16.5-19.5 atomic%.
 4. The method of claim 2, wherein the dopant content is at leastapproximately 1.65 atomic % and the barium content is at leastapproximately 29.9 atomic %.
 5. The method of claim 2, wherein the filmfurther comprises a barium to barium+dopant+copper ratio greater thanapproximately 37.5%, a dopant to barium+dopant+copper ratio less thanapproximately 2.0%, a copper to barium+dopant+copper ratio less thanapproximately 60.5%, and a rare-earth content between 16.5-19.5 atomic%.
 6. The method of claim 2, wherein the film further comprises a bariumto copper ratio greater than or equal to approximately 0.58 and arare-earth content between 16.5-19.5 atomic %.
 7. The method of claim 2,wherein the film further comprises a barium+dopant to copper ratiogreater than or equal to approximately 0.62 and a rare-earth contentbetween 16.5-19.5 atomic %.
 8. The method of claim 2, wherein thesuperconducting tape further comprises a critical current density lessthan or equal to approximately 4.2 MA/cm² at 77 K in absence of anexternal magnetic field.
 9. The method of claim 2, wherein thesuperconducting tape further comprises a critical current greater than800 A/cm-width in the 3 T magnetic field at 30K.
 10. The method of claim1, wherein the superconducting tape further comprises a lift factorgreater than or equal to approximately 4.0 at approximately 30 K in amagnetic field of approximately 3 T having an orientation perpendicularto the superconducting tape.
 11. The method of claim 10, wherein thebarium+dopant content is greater than approximately 33.0 atomic % andthe film further comprises a rare-earth content between 16.5-19.5 atomic%.
 12. The method of claim 10, wherein the dopant content is at leastapproximately 1.65 atomic % and the barium content is at leastapproximately 30.5 atomic %.
 13. The method of claim 10, wherein thefilm further comprises a barium to barium+dopant+copper ratio greaterthan approximately 38.0%, a dopant to barium+dopant+copper ratio lessthan approximately 2.5%, a copper to barium+dopant+copper ratio lessthan approximately 59.5%, and a rare-earth content between 16.5-19.5atomic %.
 14. The method of claim 10, wherein the film further comprisesa barium to copper ratio greater than or equal to approximately 0.62 anda rare-earth content between 16.5-19.5 atomic %.
 15. The method of claim10, wherein the film further comprises a barium+dopant to copper ratiogreater than or equal to approximately 0.65 and a rare-earth contentbetween 16.5-19.5 atomic %.
 16. The method of claim 10, wherein thesuperconducting tape further comprises a critical current density lessthan or equal to approximately 3.8 MA/cm² at 77 K in absence of anexternal magnetic field.
 17. The method of claim 1, wherein thesuperconducting tape further comprises a critical current densitygreater than approximately 12 MA/cm² at approximately 30 K in a magneticfield of approximately 3 T having an orientation parallel to the c-axis.18. The method of claim 17, wherein the critical current density isgreater than approximately 15 MA/cm² at approximately 30 K in a magneticfield of approximately 3 T having an orientation parallel to the c-axis.19. The method of claim 17, wherein the film has a film thickness of atleast approximately 0.9 μm.
 20. The method of claim 17, wherein thesuperconducting tape further comprises a critical current greater than800 A/cm-width in the 3 T magnetic field at 30K.